In the current 3rd Generation Partnership Project (3GPP) long term evolution (LTE) time division duplex (TDD)-Advanced systems, the same frequency bands are used for the uplink and downlink transmissions between evolved node Bs (eNodeBs) and user equipment (UE). Uplink and downlink transmissions are separated by transmitting either uplink data or downlink data at each pre-determined block of time, known as subframes, on the same frequency bands. In TDD deployment, the uplink and downlink transmissions are structured into radio frames, each 10 ms in time length. Each radio frame may comprise a single frame or two half-frames of each 5 ms in time length. Each half-frame, in turn, may comprise five subframes of 1 ms time length each. Particular designations of subframes within a radio frame for uplink or downlink transmission—referred to as uplink and downlink configurations—can be defined. The seven supported uplink and downlink configurations (also referred to UL/DL configurations, uplink-downlink configurations, or uplink-downlink ratio configurations) are shown in a table 100 of FIG. 1, in which “D” denotes a subframe reserved for downlink transmission, “U” denotes a subframe reserved for uplink transmission, and “S” denotes a special subframe which includes the downlink pilot time slot (DwPTS), guard period (GP) and uplink pilot time slot (UpPTS) fields. (See 3GPP TS 36.211 Version 10.5.0, E-UTRA Physical Channels and Modulation (Release 10), June 2012.)
LTE environments are moving toward heterogeneous deployment and/or inter-band aggregation of component carriers (CCs) with different TDD UL/DL configurations to improve communication capacity. However, under the current supported UL/DL configurations, only Subframes 3 and 8 of each radio frame are allocated for DL hybrid automatic repeat request-acknowledge (HARQ-ACK) feedback on the physical hybrid automatic repeat request (ARQ) indicator channel (PHICH) channel by the UEs. Such PHICH resources are insufficient to address the increased DL HARQ-ACK feedback requirements associated with heterogeneous deployment and/or inter-band aggregation of CCs with different TDD UL/DL configurations.